This invention relates to a swash plate compressor, and more particularly to a swash plate compressor suitable for use as a compressor for an automotive vehicle, which uses CO2 (carbon dioxide) as a refrigerant.
FIG. 7 is a longitudinal cross-sectional view of a conventional swash plate compressor.
The swash plate compressor includes a cylinder block 101 having a plurality of cylinder bores 106 formed therein, a shaft 105 rotatably supported in a central portion of the cylinder block 101, a swash plate 110 which rotates along with rotation of the shaft 105, a crankcase 108 in which the swash plate 110 is received, and pistons 107 each of which is connected to the swash plate 108 via a pair of shoes 160, 161 and slides in a corresponding one of the cylinder bores 106 along with rotation of the swash plate 110.
The piston 107 is comprised of a hollow cylindrical portion 107a for sliding in the cylinder bore 106, and a bridge 107b rollably supporting the pair of shoes 160, 161.
The bridge 107b projects radially outward with respect to the hollow cylindrical portion 107a by a connecting portion 107c extending from a bottom portion 107e of the hollow cylindrical portion 107a in a radially outward direction of the cylinder block 101.
As the shaft 105 rotates, the swash plate 110 rotates along with rotation of the shaft 105. The rotation of the swash plate 110 causes relative rotation of the shoes 160, 161 on sliding surfaces 110a, 110b of the swash plate 110, which converts rotation of the swash plate 110 into reciprocating motion of each piston 7.
As a result, the volume of a compression chamber 122 within the cylinder bore 106 changes, which causes suction, compression and delivery of refrigerant gas to be sequentially carried out, whereby refrigerant gas is delivered from the compression chamber 122 in an amount corresponding to the angle of inclination of the swash plate 110.
During this operation, the compression reaction force from refrigerant gas compressed by the reciprocating motion of the piston 107 is received by the inclined swash plate 110, so that tilting loads R1, R2 are applied on the piston 107 as shown in the figure.
The tilting loads R1, R2 are dependent on dimensions L1, L2 shown in the figure, such that the loads R1, R2 become smaller as the length L1 is longer (i.e. the length L2 is shorter). Here, L1 represents the distance between the point of application of the tilting load R1 on a top side of the piston 107 and the point of application of the tilting load R2 on a bottom side of the same, while L2 represents the distance between the point of application of the tilting load R2 and the point of application of the compression reaction force from the swash plate 110.
It should be noted that in a compressor using CO2 as a refrigerant, the difference between high pressure and low pressure is so large (approximately 15 MPa at the maximum) that the compression reaction force generated during a compression stroke of a piston is larger than in a conventional compressor using chlorofluorocarbon as a refrigerant.
Further, the delivery quantity of the compressor using CO2 is ⅙ to {fraction (1/10)} of that of the conventional compressor using chlorofluorocarbon, and the diameter of each cylinder bore 106 of the former is as small as ⅓ to xc2xd of that of the latter, so that surface pressure becomes much higher.
Moreover, the pistons 107 and the cylinder bores 106 are abraded due to sliding frictions between the pistons 107 and the respective cylinder bores 106, which are caused by the tilting loads R1, R2.
Furthermore, the edge (peripheral edge of the top surface) of each piston 7 removes lubricating oil attached to the corresponding cylinder bore 106, so that the breaking of oil film can cause seizure of the piston 107.
It is an object of the invention to reduce tilting load acting on each piston to thereby provide a highly durable and reliable swash plate compressor.
To achieve the above object, the present invention provides a swash plate compressor including a cylinder block having a plurality of cylinder bores formed therein, a rotational shaft rotatably supported in a central portion of the cylinder block, a swash plate which rotates along with rotation of the rotational shaft, a crankcase in which the swash plate is received, and pistons each connected to the swash plate via a pair of shoes and sliding in a corresponding one of the cylinder bores along with rotation of the swash plate, and wherein each of the pistons comprises a hollow cylindrical portion for sliding in the cylinder bore, and a bridge for rollably supporting the pair of shoes, the bridge projecting radially outward with respect to the hollow cylindrical portion by a connecting portion extending from a bottom portion of the cylindrical portion in a radially outward direction of the cylinder block, characterized in that the cylinder block is formed with a projecting portion projecting from a central portion of a front end face thereof toward the crankcase, within a range limited such that the projecting portion does not interfere with the connecting portion.
Since the cylinder block is formed with the projecting portion projecting from the central portion of the front end face thereof toward the crankcase, within the range limited such that the projecting portion does not interfere with the connecting portion, a point of application of a tilting load on the bottom side of the piston for tilting the piston is shifted toward the front head side of the same, whereby the distance between the point of application of the tilting load on the top side of the piston and the point of application of the tilting load on the bottom side of the same is increased. Consequently, the tilting load is reduced, whereby abrasion between the piston and the cylinder block is decreased, which enhances durability. Further, friction loss is reduced, and slidability of each piston is improved, which makes it possible to reduce the driving force of the compressor, thereby enhancing performance and reliability of the same.
Preferably, the projecting portion has a generally hollow cylindrical shape in side view.
Since the projecting portion is has a generally hollow cylindrical shape in side view, it is easy to machine the same.
Preferably, the projecting portion has a generally hollow truncated cone shape in side view.
Since the projecting portion is generally conical in shape in side view, it is easy to remove burrs produced when the projecting portion is machined, which improves machining efficiency.
Preferably, the hollow cylindrical portion has a portion of a bottom-side end thereof extended to a location radially opposed to the connecting portion.
Since the portion of the bottom-side end of the cylindrical portion is extended to the location radially opposed to the connecting portion, the bottom-side end portion of the piston is not completely received in the cylinder bore even when the piston is close to its top dead center position. Therefore, the tilting load is progressively reduced as the piston becomes close to its top dead center position.
Preferably, the projecting portion has a generally hollow cylindrical shape in side view, and the hollow cylindrical portion has a portion of a bottom-side end thereof extended to a location radially opposed to the connecting portion.
Preferably, the projecting portion has a generally truncated cone shape in side view, and the hollow cylindrical portion has a portion of a bottom-side end thereof extended to a location radially opposed to the connecting portion.
Preferably, the cylindrical portion of the piston is formed with an annular groove always radially opposed to an inner peripheral surface of the cylinder bore.
Since the cylindrical portion of the piston is formed with the annular groove always radially opposed to the inner peripheral surface of the cylinder bore, it is possible to hold lubricating oil in the annular groove. Consequently, it is possible to prevent breaking of oil film on the piston, and seizure of the same resulting therefrom.
Preferably, the projecting portion has a generally hollow cylindrical shape in side view, and the hollow cylindrical portion of the piston is formed with an annular groove always radially opposed to an inner peripheral surface of the cylinder bore.
Preferably, the projecting portion has a generally truncated cone shape in side view, and the hollow cylindrical portion of the piston is formed with an annular groove always radially opposed to an inner peripheral surface of the cylinder bore.
Preferably, the hollow cylindrical portion has a portion of a bottom-side end thereof extended to a location radially opposed to the connecting portion, and the hollow cylindrical portion of the piston is formed with an annular groove always radially opposed to an inner peripheral surface of the cylinder bore.
Preferably, the projecting portion has a generally hollow cylindrical shape in side view, and the hollow cylindrical portion has a portion of a bottom-side end thereof extended to a location radially opposed to the connecting portion, the hollow cylindrical portion being formed with an annular groove always radially opposed to an inner peripheral surface of the cylinder bore.
Preferably, the projecting portion has a generally truncated cone shape in side view, and the hollow cylindrical portion has a portion of a bottom-side end thereof extended to a location radially opposed to the connecting portion, the hollow cylindrical portion being formed with an annular groove always radially opposed to an inner peripheral surface of the cylinder bore.